NASA Technical Reports Server (NTRS) 19940024198: Selection of the Space Station Freedom (SSF) Flat Collector Circuit (FCC) insulation material

10 Pages·0.21 MB·English

by  NASA Technical Reports Server (NTRS)

SELECTION OF THE SPACE STATION FREEDOM (SSF) FLAT COLLECTOR
CIRCUIT (FCC) INSULATION MATERIAL
N94-28701
Dawn Emerson
NASA Lewis Research Center
Cleveland, Ohio
FUNCTION OF FCC:
A FLEXIBLE CABLE WHICH PROVIDES MULTIPLE ELECTRICAL
PATHS FOR THE DISTRIBUTION OF ELECTRICAL POWER FROM
CIRCUIT COMPONENTS ON THE SSF SOLAR ARRAY.
J_TayPowerDeadfadngOption Locations
PI_iCII)ING PA:,.,_,_,_.,t_,,_'!,;,l=XF.'ttb_,eE, 41
REQUIREMENTS OF THE FCC WHICH AFFECT THE SELECTION OF
THE INSULATION MATERIAL
THE FCC SHALL PERFORM AS SPECIFIED AFTER EXPOSURE TO
THE FOLLOWING ENVIRONMENTS:
ATOMIC OXYGEN EXPOSURE - TOTAL FLUENCE 5.4 x 10zzAO/CM z.
O
(15 YEARS OF EXPOSURE)
O ULTRAVIOLET RADIATION EXPOSURE - 10 SUN YEARS (2/3 OF
ILLUMINATED ORBITAL TIME OVER 15 YEARS).
THERMAL CYCLES - 87,000 THERMAL CYCLES BETWEEN :1: 100°C.
O
STORAGE LIFE - 5 YEARS SHELF LIFT UNDER FOLLOWING
o
ENVIRONMENT:
TEMPERATURE = + 10, + 40"C
RELATIVE HUMIDITY - 20 TO 60%
PRESSURE - 650 TO 810 TORR
OTHER REQUIREMENTS:
o THE FCC SHALL NOT ADHERE TO ITSELF. (BLOCKING)
o THE SURFACE OF THE FCC SHALL HAVE A SOLAR ABSORPTIVITY
< .45 BOL.
o THE SURFACE OF THE FCC SHALL HAVE AN INFRARED EMISSIVITY
> .85 AT BOL.
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DATA TO SUPPORT THE SELECTION OF THE FCC INSULATION
MATERIAL WAS OBTAINED THRU DEVELOPMENT WORK
ASSOCIATED WITH THE SA COVERLAY.
o THE SAME MATERIAL IS USED FOR THE FCC INSULATION AND THE
SA COVERLAY°
THE DEVELOPMENT WORK TO BE PRESENTED WAS DONE ON THE
SOLAR ARRAY COVERLAY MATERIAL. THE FINDINGS ARE
APPLICABLE TO THE FCC APPLICATION.
COVERLAY IS THE STRUCTURAL LAYER OF THE SOLAR ARRAY
TO WHICH THE SOLAR CELLS ARE BONDED.
COVERLAY ALSO FUNCTIONS AS THE DIELECTRIC BETWEEN THE
INTERCONNECTING CIRCUITRY ON THE SA AND THE LEO
ENVIRONMENT.
DEVELOPMENT HISTORY
INITIAL SELECTION (1989}:
SiOx COATED 1 MIL THICK KAPTON H.
INITIAL DESIGN WAS BASED ON MILSTAR AND SAFE FLEXIBLE
SOLAR ARRAY DESIGNS AND MATERIAL DEVELOPMENT WORK
PERFORMED BY LMSC UNDER LeRC CONTRACT.
TESTS PERFORMED:
SHORT EXPOSURE TO RF GENERATED OXYGEN PLASMA (1 WK).
TEST RESULTS:
SiOx COATED KAPTON EXHIBITED A DECREASE IN THE AO INDUCED
MASS LOSS RATE RELATIVE TO BARE KAPTON (REDUCTION IN MASS
LOSS RATE UP TO 100x).
TEST LIMITATIONS:
LONG DURATION TESTS NECESSARY FOR SSF APPLICATIONS WERE
OUTSIDE THE SCOPE OF THE INITIAL MATERIAL DEVELOPMENT
PROGRAM.
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INITIAL SELECTION f1989)
FURTHER TESTING FOR SSF APPLICATIONS
TESTS PERFORMED:
SIMULATED LONG DURATION AO STABILITY TESTS (SIMULATED 15 YR
EXPOSURE).
TEST RESULTS:
o SiOx COATING ITSELF DISPLAYED SUPERIOR STABILITY AGAINST AO
ATTACK.
o ANY BREAKS INITIALLY PRESENT IN COATING RESULTED IN EROSION
OF THE UNDERLAYING MATERIAL.
o TENSILE STRENGTH OF THE COVERLAY DECREASES RAPIDLY DUE TO
THE LOW TEAR PROPAGATION STRENGTH OF KAPTON.
COVERLAY APPLICATION REQUIRED A MATERIAL WITH GREATER
O
MECHANICAL STRENGTH RETENTION TO MEET SA LOAD
REQUIREMENTS.
EROSION OF THE KAPTON INSULATION MATERIAL IN THE FCC
O
APPLICATION MAY INCREASE THE PROBABILITY OF SHORT CIRCUIT
44
MODIFIED DESIGN
E-GLASS TESTING:
E_LV_t_J_IM_=_LT_ DURATION/EXPOSURE RESULTS
HUMIDITY 30 DAY AT 90% RH EXHIBITED ADEQUATE
85"C PROPERTIES FOR LONG
TERM STORAGE.
SIMULATED EFFECTIVE FLUENCE NO CHANGE
ATOMIC OXYGEN 1.5 x 102 AO/CM z IN MATERIAL
ON UNSIZED 30% EXPECTED STRENGTH
E-GLASS SSF EXPOSURE
SIMULATED AO .07 x 10z=AO/CM z 30% LOSS IN
ON SIZED E-GLASS 1% EXPECTED SSF TENSILE STRENGTH/
(S-938" SIZING} EXPOSURE STRENGTH OF SIZED CLOTH
REMAINED ABOVE
STRENGTH OF UNSIZED
CLOTH
*SlLANE SIZING (S-938) INCREASES THE TENSILE STRENGTH AND
IMPROVES THE ADHESION OF FIBERS TO SILICONE.
MODIFIED DESIGN (1990} BASELINE:
1300A SiOx COATING
1 MIL KAPTON H
1300A SiOx COATING
1.5 MIL THICK STYLE 106 E-GLASS IMPREGNATED WITH NUSIL
TECHNOLOGY CV1-2502 SILICONE
1 MIL BARE KAPTON HN
ADVANTAGES OF NEW DESIGN:
FIBERGLASS PROVIDES STRENGTH RETENTION (ASSUMES LOAD
CARRYING ROLE}.
2 LAYERS OF SiOx COATING PROTECT THE FIBERS IN THE SILICONE
MATRIX.
EVEN AFTER THE FIBERS IN THE SILICONE MATRIX ARE EXPOSED,
STABILITY OF THE GLASS UNDER AO EXPOSURE WILL AID IN
MAINTAINING TEAR RESISTANCE AND STRENGTH.
o OUTER LAYER OF SiOx PREVENTS BLOCKING.
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COVERLAY TESTING - ASSUMED END-OF-LIFE CONFIGURATION
EOL CONFIGURATION REPRESENTS WORST-CASE CONDITION
AFTER BOTH LAYERS OF KAPTON ARE ERODED AWAY,
CONFIGURATION CONSIDERED TO PRODUCE CONSERVATIVE
RESULTS.
FJJY_[B_.J__ DURATION/EXPOSURE RESULTS
1. AO EFFECTIVE FLUENCE o* EMBRITTLED REGIONS
2.9 x 10zzAO/CM z o LOSS OF TENSILE
60% SSF STRENGTH
EXPOSURE LEVEL
*RESULTS WERE NOT CONSIDERED WITH EXPECTED RESULT BASED
ON LDEF DATA, WHICH INDICATED SILICONE HAS GOOD
RESISTANCE TO AO EMBRITTLEMENT.
UV 8000 EQUIVALENT INCREASE IN TENSILE STRENGTH
SUN HRS AT 2 FROM 30-_0 LB/IN
SUNS INTENSITY NO CRACKING OBSERVED.
SLIGHT DARKENING
ENVIRONMENT DURATION/EXPOSURE RESULTS
2. AO 80% SSF RETENTION OF TENSILE
(RECENT DATA EXPOSURE LEVEL STRENGTH PROPERTIES ON
SEPARATE LOT} BOTH BOL, EOL SPECIMENS
*THE VARIATION IN TEST VALUES EXHIBITED IN AO TEST 1
COMPARED TO EARLIER DATA AND CURRENT DATA ARE
ATTRIBUTED TO EITHER:
o DEPENDENCE OF TEST CONFIGURATION
o LOT TO LOT VARIATION
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CONCLUSION
THE MOST SIGNIFICANT ENVIRONMENTAL EXPOSURE EFFECTS
ARE FROM ATOMIC OXYGEN.
THE MODIFICATION TO THE COVERLAY PROVIDE FOR GREATER
ROBUSTNESS TO THE EFFECTS OF LONG LEO EXPOSURE.
EFFECTS ON MODIFIED DESIGN ON FCC
o CHANGES TO THE COVERLAY DRIVEN BY THE NEED TO IMPROVE
THE SA STRENGTH RETENTION SERVED TO BENEFIT THE FCC:
PROVIDES BETTER PROTECTION AGAINST THE OCCURRENCE OF
,
EXPOSED COPPER CONDUCTOR.
(INITIAL DESIGN - IMPERFECTIONS IN SiOx COATING RESULTED
IN EROSION OF KAPTON AND SUBSEQUENT TEARING, LEADING
TO EXPOSED CONDUCTOR.)
*2. A. TESTS INDICATE THE MODIFIED DESIGN IS MORE RESILIENT
TO ARC TRACKING INITIATION.
B. MODIFIED DESIGN ELIMINATED FLASH OVER.
* NASA CONTRACTOR REPORT 191106, THOMAS J. STUEBER
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ARC TRACKING TESTS PERFORMED ON FCC
CHARACTERISTIC OF KAPTON:
KAPTON POLYMIDE WIRING INSULATION IS VULNERABLE TO
PYROLIZATION (CHARRING), ARC TRACKING AND FLASHOVER WHEN
MOMENTARY SHORT CIRCUIT ARCS APPEAR.
O ARC TRACKING OCCURS WHEN THE SHORT CIRCUIT ARC
PROPAGATES DOWN THE WIRE THRU CONTINUED
PYROLIZATION.
O FLASHOVER OCCURS WHEN AN ARC INVOLVING ONE PAIR
OF WIRES CHARS ADJOINING WIRING RESULTING IN
MULTIPLE FAILURES.
ARC TRACKING TEST WERE CONDUCTED BY:
GENERATING A DEFECT LOCATED BETWEEN ONE OF THE SUPPLY
1
LINES AND ITS CORRESPONDING RETURN LINE WHICH EXPOSES
A SMALL AREA OF THE COPPER RETURN LINE.
2. SAMPLES WERE PREPYROLIZED BY CREATING A MOMENTARY
SHORT CIRCUIT ARC. POWER WAS THEN TURNED OFF.
TEST WAS CONDUCTED TO DETERMINE THE MINIMUM OPEN
.
CIRCUIT VOLTAGE AND SHORT CIRCUIT CURRENT NECESSARY
TO RESTART THE ARC TRACKING EVENT.
FLASHOVER TESTS WERE CONDUCTED ON 3 SIDE-BY-SIDE ENERGIZED
CHANNELS.
FLASHOVER TEST WAS CONDUCTED BY PROMOTING THE ARC
.
TRACKING EVENT BY SHORTING THE MIDDLE CHANNEL WITH
ADJOINING CHANNELS ENERGIZED.
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ARC TRACKINGTEST RESULTS
ARCTRACKING:
A MOMENTARYSHORTCIRCUITDIDINITIATEKAPTONPYROLYSIS
AT POWERLEVELSBELOWSSFOPERATINGLEVELS.HOWEVER,
NEWDESIGNWASMORERESILIENTTOARCTRACKINGINITIATION
THANPREVIOUSDESIGN.
PREVIOUSDESIGN:
ARCTRACKINGWASINITIATEDAT THEEPOCHOFTHEFIRST
MOMENTARYSHORTCIRCUIT.
NEWDESIGN:
TYPICALLYSEVERALMOMENTARYSHORTCIRCUITSWERE
NEEDEDTOPYROLIZETHEPOLYIMIDEENOUGHTOINITIATEARC
TRACKING.
FLASHOVER:
THEFLASHOVEREVENTOBSERVEDINEARLIERDESIGNSDIDNOT
OCCURWITHTHEMODIFIEDDESIGN
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